INSIGHT ON HOW BED CONFIGURATION AFFECTS

PROPERTIES OF BED LOAD MOTION

ICSE6

Paris – August 27-31, 2012

Authors: Campagnol Jenny , Radice A. and Ballio F.

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Definition of the objective of the study

Figure 1. Conceptual representation of a bed particle trajectory consisting of three distinct ranges of scales: local, intermediate and global (Nikora et al. 2002).

Aim of the research Experimental campaign Results ICSE6 – Paris 2012

RESEARCH PROPOSAL:

Study of how different kinds of bed affect some properties of sediments, moving as bed load,

within their intermediate trajectories.

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Definition of the objective of the study

Aim of the research Experimental campaign Results ICSE6 – Paris 2012

1) KINEMATICAL PROPERTIES

Variables: Tt , L , L, Lx, Ly, Vx, Vy

Analysis:

•min, max, µ, σ, cv, Sk, Ku

•PDF

•EPD

2) TRAJECTORY STRUCTURE

Variables: L , L

Analysis:

Tortuosity (L / L )

Fractal dimension D (L ≈L D)

3) DIFFUSION PROPERTIES

Variables: x(t), y(t)

Analysis:

Diffusion exponent (σ2=t2)

L

Lx

Ly

x

y L

Figure 2. Definition sketch of some variables used to characterize intermediate particle trajectory.

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Aim of the research Experimental campaign Results

Experimental campaign

ICSE6 – Paris 2012

NOTE: Qcr,Mobile Bed=10l/s;

TEST CONDITIONS

Flow discharge Q (l/s) 8.0 11.1 11.8 12.2 12.6 13.0

Mobile uniform bed MB

Fixed Rough bed FB

FB with macro-roughness elements - low density FBLD

FB with macro-roughness elements - high density FBHD

Smooth bed SB

SB with macro-roughness elements - low density SBLD

SB with macro-roughness elements- high density SBHD

Carried out Not carried out

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Experimental set-up

EXPERIMETAL TOOLS Tool Description Note/Function

Duct

Length x width x height : 5.6m x 0.4m x 0.11m

-Recess section for MB experiments, length x height: 2m x 0.04m

Feeder

Location: close to the inlet

-Impulsive feeding

Ultrasonic Doppler Profiler

N of probes: 2 Location: upstream and downstream the measurement window

-Measurements of the instantaneous velocity profiles -Identification of bed height

Videocamera

Filmed area length x width: 0.4m x 0.25m Frame rate:26 fps

-Fixed above the duct

Magnetic flowmeter

Location: delivery pipe

-Measurements of flow discharge

Flow

Fixed bed Recess section

PVC bar

Feeder

Figure 3. Pictures of the experimental set-up. dx) Duct and feeder; sx) Videocamera.

Aim of the research Experimental campaign Results ICSE6 – Paris 2012

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Experimental set-up

EXPERIMETAL TOOLS Tool Description Note/Function

Duct

Length x width x height : 5.6m x 0.4m x 0.11m

-Recess section for MB experiments, length x height: 2m x 0.04m

Feeder

Location: close to the inlet

-Impulsive feeding

Ultrasonic Doppler Profiler

N of probes: 2 Location: upstream and downstream the measurement window

-Measurements of the instantaneous velocity profiles -Identification of bed height

Videocamera

Filmed area length x width: 0.4m x 0.25m Frame rate:26 fps

-Fixed above the duct

Magnetic flowmeter

Location: delivery pipe

-Measurements of flow discharge

Aim of the research Experimental campaign Results ICSE6 – Paris 2012

Figure 4. Sediment mixture.

SEDIMENTS Description Note/Function

Shape: : uniform quasi-spherical

Equivalent diameter: 3mm

Density: 1270 kg/m3 (PBT-plastic)

Color: black/white (95% / 5% respectively)

-The mixture of BW sediments make easier particle tracking

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Aim of the research Experimental campaign Results

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Image processing

ICSE6 – Paris 2012

INPUT:

x(t), y(t) partial global trajectories

Labeling motion/stillness

Validation

OUTPUT:

x(t), y(t) intermediate trajectories

Criterion of labeling

xt+t > xt t > 0 within the global trajectory

Figure 5. Sketch of the labeling procedure of a part of a global trajectory.

The tags “0/1” mean “stillness/motion”.

INPUT:

Sequences of images of moving sediments

Identification

Tracking

OUTPUT:

x(t), y(t) partial global trajectories

STREAMS (NOKES, 2012) :

PARTICLE IDENTIFICATION AN PARTICLE TRACKING

POSTPROCESS_PTV:

IDENTIFICATION OF THE INTERMEDIATE TRAJECTORIES

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Aim of the research Experimental campaign Results

Experimental campaign

ICSE6 – Paris 2012

NOTE: Qcr,Mobile Bed=10l/s;

TEST CONDITIONS

Flow discharge Q (l/s) 8.0 11.1 11.8 12.2 12.6 13.0

Mobile uniform bed MB

Fixed Rough bed FB

FB with macro-roughness elements - low density FBLD

FB with macro-roughness elements - high density FBHD

Smooth bed SB

SB with macro-roughness elements - low density SBLD

SB with macro-roughness elements- high density SBHD

Carried out Not carried out Analyzed

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Experimental campaign

ICSE6 – Paris 2012

Figure 6. Path of macro-roughness elements in RBLD configuration.

L=13cm

D=4cm

d=0.3cm

d=1.27

D=1.9

D/d=13.3

AD/A=0.07

Aim of the research Experimental campaign Results

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Aim of the research Experimental campaign Results ICSE6 – Paris 2012

Table 1. Parameters of the experimental tests and statistics of first and second order of the analyzed variables.

Figure 7. Images of the flume bed during the tests FB1 (lower Q, left side) and FB2 (larger Q, right side).

Results: analysis of the statistical moments

Test description

Momenta Tt L Lx Ly Vx Vy

Test Q

(m3/s) µ

(s) σ

(s) µ

(mm) σ

(mm) µ (s)

σ (mm)

µ (mm)

σ (mm)

µ (mm/s)

σ (mm/s)

µ (mm/s)

σ (mm/s)

MB1 0.011 0.52 0.39 19.17 22.24 18.56 22.22 -0.20 4.89 28.25 17.17 -0.56 9.63 MB2 0.013 0.44 0.38 16.62 22.37 16.08 22.25 0.27 4.77 27.94 18.71 0.77 10.07 FB1 0.011 0.55 0.42 20.81 23.93 20.15 23.9 0.33 5.35 29.38 16.6 0.73 9.89 FB2 0.013 0.53 0.42 22.75 28.05 22.15 28.01 0.27 5.39 32.61 20.54 0.55 9.96

FBLD1 0.011 0.47 0.37 16.73 20.36 15.78 20.13 -0.23 6.31 26.92 16.82 -0.37 12.17

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Aim of the research Experimental campaign Results

Results: Pdf and Edp

ICSE6 – Paris 2012

Figure 8. Pdf and Edp of the travelt time and lenght for Q=11.1 l/s.

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Aim of the research Experimental campaign Results

Results: Pdf and Edp

ICSE6 – Paris 2012

Figure 9. Pdf and Edp of the velocity components for Q=11.1 l/s.

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Conclusion and further steps

ICSE6 – Paris 2012

MAIN FINDINGS:

1. The comparison among data of previous studies have to done carefully;

FB can reproduce closely but not perfectly the MB;

Macro-roughness elements change the characteristics of particle trajectories and the differences could depend on their density and patchiness.

2. The relationship between the solid discharge and the length of the trajectory is not straightforward and involves the intermittent features of the process (i.e., motion and stillness of particles);

3. Under weak bed load condition, kinematic variables don’t change significantly with the discharge.

NEXT STEPS:

• Analysis of the trajectories in all different experimental sets-up;

• Analysis of the geometrical structure of intermediate trajectories

• Analysis of the diffusion properties of moving sediments within the intermediate range.

INSIGHT ON HOW BED CONFIGURATION AFFECTS

PROPERTIES OF BED LOAD MOTION

ICSE6

Paris – August 27-31, 2012

THANKS FOR YOUR ATTENTION